In the burgeoning areas of vibrational haptics, Piezo elements are rapidly becoming the actuators of choice. These elements typically require very large voltage drives in order to create a desired level of haptical information for a user. Some of the highest levels of voltages to be driven for Piezo haptics can be 200 volts peak to peak (P2P).
In addition to the large drive voltages employed to drive Piezo elements of haptics, the Piezo elements present a load to the high-voltage driver that is nearly pure capacitance, which can typically range from one nanofarad to three microfarads. This can create issues in waste heat for a driver circuit, as the load, a nearly pure capacitive load, dissipates very little heat, and therefore coupling lines within the high-voltage driver can dissipate significant heat. Moreover, the driven signal is typically an amplitude modulated signal, with a range of carrier frequencies from 100 Hz to 100 kHz.
This scenario presents challenges to a prior-art high voltage amplifier, such as used in Piezo haptics, in terms of efficiency, such as power efficiency, quiescent current, and stability.
Moreover, some typical battery values used to drive a high-voltage driver amplifier for Piezo haptics are from 3 volts to 4.2 volts. A boost converter for Piezo haptics may need to create 105 volts to generate a 200 volt p2p differentially. Therefore, in this scenario, considering the step factor and the efficiency, a current delivered to the load is multiplied by a factor of almost forty times. Therefore, keeping quiescent current to a minimum on a prior art 100-volt and above rail is a significant issue.
Therefore, there is a need in the art to address at least some of the issues associated with a high-voltage amplifier that drives Piezo haptics.